if(CheckPlayerDistanceToVehicle(0.3, playerid, vehicleid))
{
//Ваши действия
}

PHP код:
stock CheckPlayerDistanceToVehicle(Float:radi, playerid, vehicleid)  
{  
    if(IsPlayerConnected(playerid))  
    {  
        new Float:PX,Float:PY,Float:PZ,Float:X,Float:Y,Float:Z;  
        GetPlayerPos(playerid,PX,PY,PZ);  
        GetVehiclePos(vehicleid, X,Y,Z);  
        new Float:Distance = (X-PX)*(X-PX)+(Y-PY)*(Y-PY)+(Z-PZ)*(Z-PZ);  
        if(Distance <= radi*radi)  
        {  
        return 1;  
        }  
    }  
    return 0;  
}